Uncatalyzed vapor phase crosslinking reaction of cotton cellulose with formaldehyde



Dec. 8, 1970 G. K. JOARDER ET L UNCATALYZED VAPOR PHASE CROSSLINKING REACTION OF COTTON CELLULOSE WITH FORMALDEHYDE Filed NOV. 19, 1968 4 Sheets-$heet 1 LG (\J O m 3 01 9L;

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Dc. 8, 1970 G. K. JOARDER ETAL 3,545,913

UNCATALYZED VAPOR PHASE CROSSLINKING REACTION OF COTTON CELLULOSE WITH FORMALDEHYDE 4 Sheets-Sheet 8 Filed Nov. 1.9, 1968 mmm GOLAM K. JOARDER STANLEY P. ROWLAND JOHN D-GUTHRIE NOE TTORNEYS 'De.s,197o G KJOARDEF'Q mL 3,545,913

UNCATALYZED VAI OR PHASE CROSSLINKING REACTION OF COTTON CELLULOSE WITH FORMALDEHYDE Filed Nov. 19, 1968 4 Sheets-Sheet s I I DECREASES IN BREAKING AND TEAR STRENGTHS AND FLEX ABRASION RESISTANCE WITH INCREASING FORMALDEHYDE CONTENT OF FABRIC U= UNCATALYZED REACTION I=CATALYZED REACTION l I I l I 04 05 4 06 0.7 08 FORMALDEHYDE N l/ O Q Q g/ -6 8 a s a a g 8 g 3 0 HiDNHHiS DNIMVEIIzIB NOISVHEIV XEILI INVENTORS GOLAM K.JOARDER STANLEY P. ROWLAND JOHN D. GUTI-IRIE (Y? 9 BY ATTORNEYS United States Patent US. Cl. 8-116.4 2 Claims ABSTRACT OF THE DISCLOSURE Cellulosic materials having high resilience and abrasion resistance are produced through uncatalyzed vapor phase reaction with formaldehyde.

A non-exclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

Considerable interest has been shown in the attainment of a high level of resilience together with high resistance to abrasive wear in cotton fabrics by vapor-phase deposition of crosslinking agents. Primary attention has been focused on formaldehyde as the crosslinking agent and the initial study in this field [Guthrie, J. D., Am. Dyestuff Reptr. 51, pp. 507-512 (1962)] showed that cotton fabric crosslinked by the vapor-phase deposition of formaldehyde-hydrogen chloride developed high resilience at uniquely low levels of bound formaldehyde. Subsequent studies showed that the product exhibited a high uniformity of distribution of crosslinkages throughout the fiber and indicated that catalysis was unnecessary for reaction at elevated temperature.

The state of collapse or of swelling of the fiber structure at the time of the crosslinking has a well known effect upon the extent to which conditioned and wet wrinkle recovery angles are developed in the fabric. For maximum conditioned wrinkle recovery angles (most often, together with high wet-wrinkle recovery angles), the crosslinkirig reaction is conducted with the fiber structure in apredominantly collapsed or unswollen condition; with the cellulose in such a state, the rate of diffusion of reagents into and throughout the fiber structure is retarded (especially relative to the rate at which the formaldehyde reacts with the cellulose) and a pronounced tendency exists for the development of a heterogeneous distribution of crosslinkages, predominantly a concentration of linkages in the peripheral region.

By the process of this invention it is shown that the slower (uncatalyzed) reaction involving vapor phase deposition of reagents produced the fabric having higher wrinkle recovery angles. This superiority is attributed to a more effective placement of crosslink-ages, primarily a more uniform distribution of linkages throughout the fiber structure. It is also shown that the cellulosic fabric under goes a lower degree of molecular degradation during the uncatalyzed reaction in terms of retention of strength properties.

High uniformity of distribution of crosslinkages in the fiber structure of cotton cellulose has been observed previously and shown to characterize the formaldehyde-modified cotton prepared by the vapor-phase reaction conducted at room temperature. This uniformity which accounts for the attainment of the high wrinkle recovery angles at the very low formaldehyde contents now clearly appears to be the consequence of the slow reaction of formaldehyde- Patented Dec. 8, 1970 hydrogen chloride vapors with the cotton at ambient temperatures. Arceneaux et al. [Arceneaux, R. L., Fujumoto, R. A., Reid, J. D., and Reinhardt, R. M., Mm. Dyestulf Reptr. 51, pp. 559566 (1962)] required higher formaldehyde contents for a given wrinkle recovery angle when the same reaction was accelerated by elevation of temperature or of catalyst concentration. This high requirement of formaldehyde for attainment of a specific wrinkle-recovery angle in the nonaqueous process of crosslinking with formaldehyde appears also to be due primarily to the heterogeneous distribution of linkages known to develop during these reactions.

The uncatalyzed reaction of formaldehyde with cotton cellulose proceeded slowly at 125 C., reaching a bound formaldehyde content of 0.75% in the fabric at approximately 12 hours of reaction time. The reaction catalyzed by boric acid proceeded significantly more rapidly but leveled off after six hours of reaction at a formaldehyle content in the fabric of approximately 1%. The shape of the initial portion of the curve for the catalyzed reaction suggests that one-two hours at the 125 C. temperature may be required to bring the reagents to characteristic concentrations in the vapor phase. See FIG. 1 of the accompanying drawing which illustrates the rates of incorporation of bound formaldehyde into cotton fabric from catalyzed and uncatalyzed reactions.

At a specific formaldehyde content in the fabric, conditioned and wet-wrinkle recovery angles of the fabric from the uncatalyzed crosslinking reaction are consistently higher, by approximately 25 (W-l-F), than those for the fabric from the catalyzed reaction. See FIG. 2 which illustrates the development of conditioned and wet wrinkle recovery angles with increasing formaldehyde content in the fabric from catalyzed and uncatalyzed reactions, and from a 24-hour catalyzed reaction.

The following examples illustrate but do not limit the scope of this invention.

EXAMPLE 1 A cotton fabric, bleached printcloth, weighing about 3.5 oz./yd. was desized, scoured, and bleached. Samples of the fabric, 12 inches by 18 inches, were dried in an oven and suspended in glass tubes in the form of a loose roll. Paraformaldehyde was placed in the bottom of the tube in a weight ratio of 1:20 with the fabric. The tubes were sealed and were heated in a forced draft oven at 125 C. for various periods of time. FIG. 1 shows the results 'of these reactions. Each data point is the result of a separate reaction. At the end of each reaction time, the seal of the tubes was broken and the fabric was rinsed in hot water.

EXAMPLE 2 A cotton fabric, bleached printcloth, weighing about 3.5 oz./yd. was desized and scourced. Samples of the fabric, 12 inches by 18 inches, were dried in an oven and suspended in glass tubes in the form of a loose roll. Paraformaldehydezboric acid:cotton fabric were employed in the weight ratio of 1:1:20. The reagents were placed in the bottom of the tube and the tubes were sealed. The tubes were heated in a forced draft oven at 125 C. for various periods of time. FIG. 1 shows the results of these reactions. Each data point is the result of a separate reaction. At the end of each reaction time, the seal of the tube was broken and the fabric was rinsed in hot water.

Reactions of formaldehyde in the vapor phase with cotton cellulose in the form of loose fibers, yarn, or fabric may be conducted over the range of 225 C. As the temperature of the reaction is raised, it is desirable to introduce water vapor into the systems to facilitate the diffusion of the reagents into the cellulose fibers. At the highest level of temperature, it is generally desirable to control the moisture content of the system so that the weight ratio between the water and the formaldehyde is about to 2 and the weight ratio between the cellulose and formaldehyde is about 2 to 100.

The moisture may be introduced into the reaction as ambient moisture in the cellulose, as water or as steam. The formaldehyde may be supplied as paraformaldehyde or vapors thereof. The substrate for the reaction may be cellulose in any form but especially cellulosic fibers such as those of cotton, linen, rayon, etc.

As indicated by a comparison from FIGS. 1 and 2, it is not necessary to continue the reaction any longer than to incorporate the desired level of bound formaldehyde. This reaction period depends on the level of found formaldehyde desired and the corresponding properties sought. In general, the reaction periods may be as follows: 15 hours at 110 C., 8 hours at 125 C., 4hours at 140 C., and only a few minutes at 225 C.

The advantages, uniform distribution, minimal molecular degradation and resilience of the products, from the uncatalyzed reaction hold over the range of conditions described above.

The uncatalyzed reaction of formaldehyde with cotton cellulose proceeded slowly at 125 C., reaching a bound formaldehyde content of 0.75% in the fabric at approximately 12 hours of reaction time. The reaction catalyzed by boric acid proceeded significantly more rapidly but leveled off after six hours of reaction at a formaldehyde content in the fabric of approximately 1% (FIG. 1).

At a specific formaldehyde content in the fabric, conditioned and wet wrinkle recovery angles of the fabric from the uncatalyzed crosslinking reaction are consistently higher, by approximately 25 (W+F), than those for the fabric from the catalyzed reaction (FIG. 2).

Fiber structure was examined in electron micrographs of (a) these cross-sections before and after immersions in 0.5 M cupriethylenedia-mine hydroxide (cuene) for 30 minute and (b) ultrathin sections of fibers which were prepared by a modification of the methacrylate expansion technique to separate the fiber into concentric layers. It has been shown that unmodified cotton leaves little or no residue in (a) and develops a high degree of expansion in (b); the amount of residue in (a) increases and the extent of expansion in (b) decreases as crosslinks are introduced into the cotton fiber.

Breaking strength, tear strength, and flex abrasion resistance decrease with increasing formaldehyde content in the fabrics. Fabric from both the catalyzed and the uncatalyzed reactions show the same relationship between strength and bound formaldehyde content. See FIG. 3 which illustrates the decreases in breaking strength, tear strength, and flex abrasion resistance with increasing formaldehyde content of the fabric from catalyzed and uncatalyzed reactions.

The lower degree of molecular degradation during the uncatalyzed reaction was confirmed in terms of retention of strength properties for samples of fabrics subjected to conditions similar to those for the reaction described above but in the absence of formaldehyde. Small decreases in tear strength and moderate decreases in breaking strength occurred as a consequence of extended periods of heating in the absence of formaldehyde and catalyst. More pronounced decreases occurred in tear strength and breaking strength when the fabric was heated in the presence of boric acid. See FIG. 4 which illustrates the decreases in breaking and tearing strength with increasing duration of heating of the fabric in catalyzed and uncatalyzed reactions.

We claim:

1. A process for the attainment of a high level of resilience together with high resistance to abrasive wear in cellulosic textile materials comprising:

reacting a cellulosic textile material with formaldehyde in the vapor phase in the absence of a catalyst in a closed system containing formaldehyde and water at a temperature from about to 225 C. in which the ratio of the components by weight is about 2 to 100 between the cellulosic material and the formaldehyde and about 0 to 2 between the water and the formaldehyde.

2. The product produced by the process of claim 1.

References Cited Joarder et al.: Textile Research Journal, vol. 37, pp. 1083-1084 (1967).

GEORGE F. LESMES, Primary Examiner I CANNON, Assistant Examiner 

